Various surgical plates have been employed in the treatment of traumas to facial or cranial bone structure, plastic surgery, reconstructive facial surgery, and the like to hold the bone sections or fragments in place during the healing process. The surgical plates are positioned against the surface of the bone sections which must be held together and fixed to the bone by mechanical fasteners such as bone screws, wire sutures or other fasteners which secure the plate to the bone surface. The fasteners are securely pressed or embedded in the bone to prevent the surgical plates from being pulled away from the surface of the bone sections. U.S. Pat. Nos. 4,966,599 and 5,290,281 disclose examples of bone stabilization plates which are secured to the bone structure, for example facial or cranial bones, by bone screws. U.S. Pat. No. 4,655,203 discloses a surgical device for immobilization of bone fracture which includes a stiff plate and stiff fixing elements which may be pressed into notches formed in the bone.
In such procedures as rotator cuff surgery and hand tendon surgery, tendons or other soft tissues are fixedly secured to bone. The tendons or other tissue are often secured to bone by feeding the soft tissue through holes formed in the bone and suturing the tissue in place. Another method of securing soft tissue to bone employs a fixation device which essentially tacks the tendon to bone. Unless the tendon or other soft tissue is completely immobilized, the fixation device must be securely embedded in the bone to hold the tendon stationary against the bone surface, resisting those forces tending to pull the tendon away from the bone surface, until the tendon has become attached to the bone. Another method of securing tendons and other soft tissue to bone uses a fixation device with an attached suture. Once again, the fixation device must be securely embedded in bone to resist forces tending to pull the tissue away from the bone surface. In various facial surgery procedures, soft tissue is surgically lifted or moved and then secured to bone by suturing and the like to hold the tissue in the desired position during the healing process. These tissues are generally subjected only to gravitational forces or other forces parallel to the surface of the bone, they are not exposed to forces tending to pull the tissue outwardly away from the bone.
Surgical plates must be securely affixed to bones which may be exposed to various tensile and bending forces during the healing process to prevent the plate from being pulled outwardly away from the bone. If the fasteners do not securely engage the bone, the applied stresses may have a tendency to pull the fasteners from the bone. Facial and cranial bone sections, on the other hand, are generally not exposed to such tensile and bending stresses. Instead, the bone sections are primarily subjected to forces tending to spread the bone sections apart or to cause lateral slippage of the bone sections along the fracture line. Since the applied forces are substantially parallel to the bone surface, the fasteners need only anchor the surgical plates to the facial or cranial bones to hold the bone sections in place. The additional security provided by securely embedding the fastener in bone and actually securing the plate to the bone surface is often not required with facial and cranial bones and of bones at other sites.
Securely embedding screws, nails and the like in bone is a time consuming and labor intensive process, considerably extending the time required to complete the operation. Even when the fasteners are initially inserted into pre-drilled holes, care must be taken to ensure that the desired orientation of the fasteners is maintained. Moreover, embedding the fasteners in bone may subject the relatively fragile facial bones to additional unnecessary stress. Surgical fasteners such as screws and the like require expensive manufacturing techniques because of the small size of the fastener. Minimizing the size of the plate and fastener would minimize the size of the surgical area and the amount of bone which must be exposed. However, the reduced size of the screws and other fasteners is limited because the fasteners have sufficient strength to engage bone and securely attach the plate to the bone. Using a fixation device which anchors the surgical plate to the bone, but does not securely affix the plate to the bone surface, would avoid the disadvantages associated with embedding the fastener in bone. Such a fixation device would also be particularly useful in other types of procedures where the fixation apparatus may be employed to affix soft tissue to bone.
The surgical plates and associated fasteners employed for bone fixation have been fabricated of materials such as titanium, stainless steel, vitalium, chrome cobalt, and suitable bio-compatible polymeric materials. Unless removed by surgery, the plates and fasteners formed of these materials permanently remain in the patient's body. The surgical plates and internal fastening members may cause various unpredictable problems if left intact as the bone dynamically reacts to the foreign bodies over time by molding to the shape of the foreign body, forming deposits on the foreign body, and responding to stress. The foreign bodies also provide potential cites for infection. Migration of the foreign body presents another problem if the surgical plate and/or fasteners are left in the patient's body. This problem is of particular concern when the patient is an infant or young child, where the considerable mount of skull growth has resulted in significant migration of foreign body to the extent where the plate has entered the brain.
Forming the plate and/or fasteners of a material which may be absorbed by the body over time would allow the foreign materials to be removed from the patient's body without requiting a second operation. U.S. Pat. Nos. 5,655,203, 4,905,680, 4,966,599, 5,275,601 and 5,290,281 describe forming the surgical plates and/or fasteners of absorbable materials. Fabricating a bone screw or other mechanical fastener out of absorbable polymers is often difficult because the absorbable fastener has a tendency to prematurely slip from the bone. Moreover, because of their reduced size, forming absorbable bone screws for the fixation of plates to facial and cranial bones is even more difficult. To achieve the desired strength, the absorbable screws must be larger in size than a comparable metal screw. A fixation device for the fixation of surgical plates to bone which may be easily manufactured of an absorbable material and reliably used is highly desirable.